Paper sludge ash (PS ash) discharged from Fuji area, Shizuoka prefecture reach about 160, 000 tons/year. Therefore, the development of a technique for utilizing of PS ash is essential for recycling waste materials.
PS ash collected in Fuji area has little of SiO
2 and much Al
2O
3, CaO, in comparison with the general material of the artificial zeolite (e. g. coal fly ash). PS mainly consists of calcite, talc and kaolinite, which are originally present in paper. These minerals are converted to gehlenite, meta-kaolinite, meta-talc and lime by incineration. For this reason, the PS ash has excess Ca and low Si containt.
We synthesized an artifical zeolite from the PS ash by the “Si-added method” to exclude the effect of excess calcium present in the ash. Furthermore, we studied the reaction conditions such as temperature, time and the alkali used, and found optimal synthesis conditions. Chemical and mineralogical characteristics of the synthesized zeolite were then investigated. It was found that an NaP 1-type zeolite was synthesized in an autoclave by processing at 120°C for 2 hours using a 3.5M meta sodium silicate (Na
2SiO
3) solution.
The characteristic of Si and Al dissolved in a diluted NaOH solution shows a characteristic property of zeolite. The PS ash, coal fly ash and Shirasu were classified to S type (Si/Al<0.5), P1 type (0.5<Si/Al<2), and P2 type (Si/Al>2), respectively, in terms of the characteristic solubility of Si and Al in diluted NaOH solutions. For zeolite synthesis, the PS ash was found to require more Si to meet the synthesis condition because the PS ash had a low Si and a high Ca content. As it was, Ca silicate (CSH) was generated and zeolite synthesis was prevented. Shirasu was chosen as a material providing complementary Si. Ca in the PS ash reacted successfully with the Si in the added Shirasu to generate zeolite.
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